What should I do about having conveyed incorrect information that I thought was a Sunnah of the Messenger of Allah, peace and blessings be upon him, and does this fall under the threat of lying about him?

It is reported that the Prophet, peace and blessings be upon him, performed Umrah immediately upon entering Mecca. The claim that resting before Umrah is part of the Sunnah is incorrect. However, there is no harm for someone who is tired and wishes to rest. As long as you did not intentionally err, there is no sin upon you, for Allah Almighty says: (And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended) and Allah Almighty says: (Our Lord, do not impose blame upon us if we have forgotten or erred). However, you must be careful thereafter not to acquire knowledge from just anyone.